As electric vehicles need to run under complicated road conditions and environment conditions, an in-vehicle battery as a power of the electric vehicles needs to adapt to these conditions. Especially when the electric vehicles are in a low temperature environment, the in-vehicle battery needs to have excellent performances of discharging and charging in the low temperature environment and high input/output power. In general, a resistance and a polarization of the in-vehicle battery may be increased in the low temperature, which may reduce a capacity of the in-vehicle battery. Therefore, in order to keep the capacity of the in-vehicle battery in the low temperature, electric vehicles are provided with a heating circuit of the in-vehicle battery.
FIG. 1 is a schematic diagram of an electric vehicle running control system according to the prior art. As shown in FIG.1, the heating circuit F is connected with the in-vehicle battery E to form a heating loop. By controlling an energy to flow between the in-vehicle battery E and the heating circuit F so as to heat a damping element in the heating circuit F, the in-vehicle battery E is heated, which increases the charging and discharging performance of the in-vehicle battery E.
However, if the in-vehicle circuit needs to be heated as the electric vehicle is running in low temperature, as a load capacitor C also needs to supply power for a vehicle load R continuously, the heating circuit F and the load capacitor C will work simultaneously. Then, the working of the heating circuit F may cause the voltage of the in-vehicle battery E to fluctuate violently (even to become a negative value), and meanwhile the heating circuit may not work normally due to the influence of the loading circuit, as shown in FIG. 2. FIG. 2 is a schematic diagram of voltage waveforms of the heating circuit F and the load capacitor C in FIG. 1, in which VF is a voltage of the heating circuit F, and VC is an output voltage of the load capacitor C.